Composite piezo-electric crystal device



. June 24, 1930. A. M L. NICOLSON COMPOSITE PIEZ-OELECTRIC CRYSTAL DEVICE Filed Dec. 20', 1926 INVENTOR\ ALEXANDER Mc LEAN NICOLSON ATTORNEY Patented June 24, I930 ENT ALEXANDER MGLEAN NIGOLSON, OF NEW YORK, N. 2., ASSIGNOR, BY MES NE ASSIGN- MENTS, TO EEDERAL TELEGRAPHCOMPANY, A CORPORATION OF CALIFORNIA COMPOSITE PIEZO-ELECTRIC CRYSTAL DEVICE Application filed December 20, 192-6. Serial No. 155,898.

This invention relates to a piezo-electric device, adapted and arranged to be utilized in connection with electric circuits, and to a method of'producing the same. It has been known for. some time that crystals of certain substances such as Rochelle salt, quartz, tourmaline, and the like, produce an electro motive force if subjected to physical stress or movement, and conversely, produce physical stresses or movement in response to the impression of an electro-motive force upon them.

Such crystals are capable of wide use and application in the electrical arts, and particularly in those arts which deal with the generation, transmission and utilization of alternating currents jor potentials, whether 7 of audible frequency or of the highest radiofrequency. Many'of such uses are particularly pointed out in patent -No. 1,495,429 granted to me on May 27, 1924.

In the past, dificulties have been encoun-j tered in the use of comparatively large crystals, and crystals of unusual shape whether natural or' grown. It has been found comparatively ,diflicult to obtain and maintain large crystals in the case of crystals made by growth from a solution of the mother liquor. such as Rochelle salt crystals. The large crystals require more time to grow thanthe small ones, and moreover, they seem to be considerably more fragile and tend to develop cracks and flaws even before the crystals have been efiectively cured and hardened.

In the case of natural crystals. such as quartz and tourmaline, etc., it is clear that.

the diificulty and expense of preparing crystals increases greatly with the size, and the liability of accidental injury in the use of the crystal is much greater.

It is an object of thisinvention to provide a piezo-electric element and a method of fabricating the same whereby the element may be given any desired size, shape, and natural frequency, b utilizing fragments of crystals,

small crysta s, nuclei, and the like secured together to form a single entity so that the piezo-eleetric effect of the components may be integrated. I Y

It is a further object of this invention to provide a composite piezo-electriecrystal and a method of fabricating the same, whereby a piezo-electric crystal of comparatively large size or of unusual dimensions or proportions may be produced, without the delay incident to the growth and curing of such crystals, and

without the time, expense, and wastage involved in cutting and grinding natural crystals, which fabricated crystals may be of the most eificient ratio of length/depth consistent with mechanical strength of the resultant structure. i

It is a further object of this invention to provide a crystal and a method of producing the same which shall be relatively strong and rugged. and not easily subject to breakage if handled roughly. i

It is a still further object of this invention to provide a crystal and method of producing the same from fragments and waste pieces Fig. 2 is a view of the same after comple-,

tion,

Fig. 3 is a diagrammatic view showing the principles to be followed in assembling acom: posite crystal according to my invention,

Fig. 4 is a diagrammatic View of a composite crystal fabricated according to my invention, showing the method of arranging electrodes, and Fig. 5 is a diagrammatic view similar to Fig. 4, but showing a modified arrangement of electrodes.

In accordance with my invention, I provide a crystal of any desired size and shape, and of any desired natural frequency, and adapted to one, two, or three modes of vibration; that is, longitudinal, transverse, or torsionaL-by fabricating it from crystal fragcan crystals, which may be distinguished from ments, units, or nuclei, by properly choosing duced. Provision is made for the connection the fragments, units or nuclei, and by as- ,of electrodes, which will preferably be moldsembling them in a manner to be hereinafter ed in place upon the individual crystals, and explained, and securing them firml desired position, as for example by c amping, from which the charges may be led from or to or bysetting the crystals into, or arranging the individual crystals. upon them, a matrix or binder of the proper After the various component crystals have nature to hold the crystals firmly and havbeen properly arranged in the mold as deing the-same elastic properties as th so thatstress waves are-transmitted therecrystals and'allowed to congeal, therebysein the likewise rovisionis made for terminals to or ecrystals scribed, the binder may bepoured upon the through and impressed upon each of the curing the assembly of component crystals c stal components. I V

n addition, I provide mechanicalor elechandled as a sing earystal. It will be clear trical connections between the crystals, and. that such composite crystals may be built up also provide the necessary electrodes arto possess, as a monolithic structure, any derang in the r p manner $0 hat the desired natural frequency. Likewise, they piezo-electric e ects of the various crystals ay b built u or fini hedin any shape'suit, y be i g d utilized- 1? eXamed to one or two or three modes of vibration, ple, in the case of Rochelle salt crystals, the longitudinal, transverse,

crystals are arranged with their A, B and C Also, the electrodes, as will be understood,

however, in the ease 6r crystalscwhich are from the crystals, or may, as already stated, found in right-handed and left-handed? b found within the tructure.

y The binder or matrix, as already stated, each other as is kn wn in h 31 1 1S I1eCeS- may be piezo-electrically inactive, such for sary in fabricating a crystal according to instance as hard wax, in which case the space my invention; to utilize all of one species f in'the mold wil,l.be filled as far as possible crystal. 3 I with crystal fragments, or it may be piezo- Accordingly, whether the comp s cryselectrically active, such as Rochelle salt tal is desired for a transmitter or receiver, lt, comprising Rochelle salt which has that is, for generator or motor operatlon, beenheated to'a temperature controlled ac- .oups or clusters of crystals of any or dlfcording to the amoimtof water of crystallizaering time constant, electrical or mechamtion which it is desired to Fetain in the melt, cal, may be connected electrlcally or mechanin which case the binder molecules themselves ically t g h r, al -th ir girdles g electllmay largely constitute the crystal, being orically integrated'in association with their elec nted and integrated, as for instance by the trically connected basal planes at one or both provi ion of a relatively small number of j ends; any volumetric crystal structure may ystals, used as seeds, in contact with the I be mechanically grouped, preferably in p rt liquid massof Rochelle salt melt while the m t c mp g er r both, in ny latter is solidifying; It i obvious that the configuration, of a plurality or multiplicity method of usin seed crystals for orienting of ry l f ag nts, units, or nuclei, or the particles 0 piezo-electrically active sub: crystals of such sizeas to be inconvenient for stances during solidification may be app-lied 'mounting and use, by methods heretofore' to other such substances besides Rochelle known in. the art. The cement,- binder, or alt,

7 matrix maybe a suitable fluid medium which- Referring now to Fig. 1, 3 designates a may be poured around the component parts, mold within which'the composite crystal 1s and permitted to solidify,-s uch as hard wax, 'to'be prepared, and as alread stated andwhich w1ll not destroy the crystal fragb f any d i d h p an siz although 150 it may inents, or it may be'a,plowl ct y active herein shown as rectangular. A streanr'of medium, such fnr example as Rochelle salt binder 2 is poured from a suitable container 1 cemen c mprlsmg Rochelle Salt O Y Ch into the mold 3 around, about and over crystal other elastic transnnsslon o 'aboutvblle fouljth P the Watel has been 19- .4, having electrodes 5-and- 6 aflixed thereon moved by heating. Care should ,be aken In on opposite sides, crystal 10, having electrodes selecting the cement,- binder, or matrix to Hand 12, preferablyof wire mesh or metal' choose one having correct longitudinal and foil,-on op osite sides thereof, and or tal 16 propertles the necessary having ele rodes 17 and18 on opposi e sides S W V 110 l h S thereof. Ejlectrodes 5 and 6 are provided with lBdv crystal units. conductors 7 and 8 connected thereto, elec- :"I'he' crystal fragments, 11111 58, r 111 trodes 11 and 12 with conductors 13 and 14, from which the composlte cryst 1 to be f and electrodes 17 and 18 with conductors 19 Heated may for exa p e be properly selectand 2O.' Leads 7, 13, and 19 may be coned with reference to constitution, and pro 7 3 nected together, as also 'leads8, 14, and 20',

erlyarrange d and oriented Within a mod whereby the 'iezo-electric action of the vaof the shape of the crystal desired to beprorious compongnts is integrated.

into one single physical entity, which may be and torsional.

axes respectively-parallel." It is understood, may be applied externally, even 'in'sulated After the binder has set, the composite crystal may be removed from the mold and will present the appearance of Fig. 2. It will be apparent that it may be handled just as if it were a single crystal. In fact, in the case of large or odd shaped crystals, it is clear that my composite crystal is physically very much stronger than a corresponding single crystal and may be handled with much less care, since it is less expensive and easier to reproduce.

Referring now to Fig. 3, I have shown diagrammatically the proper grouping of a number of crystal fragments, units, or nucei, wherein reference character 00 designates the analogous poles and y the antilogous poles of the individual portions constituting a composite element. The crystal units are selected having opposite poles by which the crystal units are oriented to the relationship designated in Fig. 3. The crystal units are positively-secured in the selected relationship illustrated in Fig. 3 while the binder is being poured around the elements and until the binder has commenced to congeal at which time the securing means may be withdrawn without dislocation of the crystal elements.

- Referring now,to Fig. 4, I have shown a number of crystals 22, 23, 24 and 25, grouped to form a composite crystal, the individual crystals being provided with electrodes on opposite poles, such as 26 and 27 on crystal 22, and corresponding electrodes on the crys-- tals 23, 24 and 25. The corresponding elec trodes 26, 28, 30 and 32, are connected together through master conductor 34, and similarly electrodes 27, 29, 31 and 33 are connected together through master conductor 35. It will be seen that by impressing stress waves upon the composite crystal, each of fthe component crystals will be subjected to stress and the piezo-ele'ctric effects will be integrated. Similarly, by subjecting the electrodes 34 and 35 to fluctuating potentials, such potentials will be impressed upon the individual crystals, and the motional or stress efl'ect of all the crystals will be integrated.

Referring to Fig. 5, I have shown the crys tals 22, 23, 24 and 25 as before, but in this instance the crystals are provided with girdle electrodes, and have their basal planes electrically connected. For example, crystal 22 is provided with girdle electrode 36, and end electrode 37, crystal 23 with girdle electrode 38 and end electrode 39, crystal 24 with girdle electrode 40 and end electrode 41, and crystal 25 with girdle electrode 42 and end electrode 43. The girdle electrodes 36, 38,40, and 42 are connected to master conductor 34, and the end electrodes 37', 39, 41 and 43, are connected to master conductor 35, from which it will bev understood that this is merely by way of example and that any number of component. crystals of heterogeneous shape and size nay be used.

It is also to be understood that while I have described in detail the assembling of component Rochelle salt crystals into the composite device, that this is by way of example, and that it is within the scope of my invention to use fragments of quartz,tourmaline and other substances, and that in each case the particular binder to be used will be chosen with respect to the crystal components with which it functions.

I claim:

1. A piezo-electric device comprising a plurality of optically similar piezo-electric crystals of heterogeneous size and shape physically secured in a single entity by means of a homogeneous binder surrounding each of said crystals and extending between the interstices with their principal axes parallel to each tals completely embedded in a matrix of elastic properties similar to those of said crystals, said crystals being oriented so that their corresponding principal optical axes are respectively substantially parallel each to each and being electrically connected so that piezoelectric efiects of said crystals are integrated.

4. A piezo-electric device comprising a plu rality .of piezo-electric crystals secured in a matrix to form asingle entity, said matrix completely surrounding said crystals and filling the interstices therebetween, said crystals being oriented so that their corresponding principal optical axes are substantially parallel respectively each to each, and said crystals being electrically connected so that the piezoelectric efiects of said crystals are integrated.

5. A piezo-electric device comprising a plurality of piezoelectric crystals secured 1n a matrix to form a single entity, said matrix ill) being com osed of piezo-electrically active material. erived from materials haying piezo-electric properties similar to the lezoelectric properties of said stals, sai crystab being oriented so that t eir corresponding rincipal optical axes are substantially para el respectlvely each to each, and said electrically connected so that crystals bein g the piezo-elec ric effects of said crystals are integrated.

6. A piezo-electric device comprising a plurality of piezo-electric crystals secured m a matrix 'to form a single entity, said matrix being com osed of piezo-electrically active material erived from materials having piezo-electrio properties similar to the iezoelectric properties of said crystals, sai matrix having its constituent particles oriented optically in substantially the same manner by contact during solidification from a liquid state with one or more seed crystals of the material from which said piezo-electrically active matrix is derived, said first mentioned crystals being oriented sothat their corres'ponding principal optical axes are substantially parallel respectively each to each, and said crystals being electrically connected soi that the piezo-electric efiects of said crystals are integrated.

.In testimony whereof I hereunto aflix my signature.

ALEXANDER MOLEAN NICOLSON. 

